If you fly up to the clouds and enter the lower portion of the cloud, the terrain will stop being rendered and you can see the sky below the world.
Update:
After playing around with it a little bit, if your Y is anything below 180, the terrain will no longer load while in the cloud. Upon leaving the cloud / the cloud moving away from you, even if you don't move yourself, the terrain will start being rendered again.
Environment
(from the Minecraft debug screen)
Java: 1.6.0_65 64 bit
Display: 1440*852 (Intel Inc.)
Intel HD Graphics 4000 OpenLG Engine
Linked issues
Comments 2
duplicate of MC-50875
Can you post a screenshot when it happens with the debug screen up (F3)?